Association biasing for a heterogeneous network (HetNet)

ABSTRACT

A method for association biasing at a mobile device in a heterogeneous network (HetNet) is disclosed. The method can include the mobile device receiving coordination set information from a macro node in the HetNet. The coordination set information can include at least one low power node (LPN) identifier of at least one LPN. The mobile device can receive a request from the macro node to apply a specified reference signal (RS) biasing. The mobile device can apply the specified RS biasing to an LPN RS measurement derived from a LPN RS received from an LPN having an LPN identifier in the received coordination set information. The mobile device can associate the mobile device with the LPN when the LPN RS measurement with the specified RS biasing exceeds an association threshold.

BACKGROUND

Wireless mobile communication technology uses various standards andprotocols to transmit data between a transmission station and a wirelessmobile device. Some wireless devices communicate using orthogonalfrequency-division multiplexing (OFDM) combined with a desired digitalmodulation scheme via a physical layer. Standards and protocols that useOFDM include the third generation partnership project (3GPP) long termevolution (LTE), the Institute of Electrical and Electronics Engineers(IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly knownto industry groups as WiMAX (Worldwide interoperability for MicrowaveAccess), and the IEEE 802.11 standard, which is commonly known toindustry groups as WiFi.

In 3GPP radio access network (RAN) LTE systems, the transmission stationcan be a combination of Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs,enhanced Node Bs, eNodeBs, or eNBs) and Radio Network Controllers(RNCs), which communicates with the wireless mobile device, known as auser equipment (UE). A downlink (DL) transmission can be a communicationfrom the transmission station (or eNodeB) to the wireless mobile device(or UE), and an uplink (UL) transmission can be a communication from thewireless mobile device to the transmission station.

In homogeneous networks, the transmission station, also called macronodes, can provide basic wireless coverage to mobile devices in a cell.Heterogeneous networks (HetNets) are used to handle the increasedtraffic loads on the macro nodes due to increased usage andfunctionality of mobile devices. HetNets can include a layer of plannedhigh power macro nodes (or macro-eNBs) overlaid with layers of lowerpower nodes (micro-eNBs, pico-eNBs, femto-eNBs, or home eNBs [HeNBs])that can be deployed in a less well planned or even entirelyuncoordinated manner within the coverage area of the macro nodes. Themacro nodes can be used for basic coverage, and the low power nodes canbe used to fill coverage holes, to improve capacity in hot-zones or atthe boundaries between the macro nodes' coverage areas, and improveindoor coverage where building structures impede signal transmission.Inter-cell interference coordination (ICIC) or enhanced ICIC (eICIC) maybe used for resource coordination to reduce interference between thetransmission stations (or nodes), such as macro nodes and low powernodes. In ICIC an interfering node (or an aggressor node) may give upuse of some resources in order to enable control and data transmissionsbetween a victim node or victim mobile device.

The transmission stations, such as the macro nodes and/or lower powernodes (LPN), can also be grouped together with other transmissionstations in a Coordinated MultiPoint (CoMP) system where transmissionstations from multiple cells can transmit signals to the mobile deviceand receive signals from the mobile device.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure; and, wherein:

FIG. 1 illustrates a block diagram of a heterogeneous network (HetNet)including a plurality of coordination sets each with a macro node and alow power node (LPN) using range expansion in accordance with anexample;

FIG. 2 illustrates a block diagram of a heterogeneous network (HetNet)including a plurality of coordination sets each with a macro node and alow power node (LPN) and applying range expansion to the LPN in the samecoordination set as the macro node and in accordance with an example;

FIG. 3 illustrates a block diagram of a heterogeneous network (HetNet)including a plurality of coordination sets each with a macro node and alow power node (LPN) and applying range expansion in an associationbetween the macro node and the LPN in the same coordination set inaccordance with an example;

FIG. 4A illustrates a block diagram of an inter-site coordinatedmultipoint (CoMP) system with non-cooperating transmitting stations inaccordance with an example;

FIG. 4B illustrates a block diagram of an intra-site coordinatedmultipoint (CoMP) system with a low power node (LPN) in accordance withan example;

FIG. 5 depicts a flow chart of a method for association biasing at amobile device in a heterogeneous network (HetNet) in accordance with anexample;

FIG. 6 illustrates a block diagram of a macro node and a mobile devicein accordance with an example; and

FIG. 7 illustrates a diagram of a mobile device in accordance with anexample.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular examples only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.Numbers provided in flow charts and processes are provided for clarityin illustrating steps and operations and do not necessarily indicate aparticular order or sequence.

Example Embodiments

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

A heterogeneous network (HetNet) can include a macro node and at leastone low power node (LPN). The macro node can be grouped with the atleast one LPN in a coordination set. The macro node can provideinter-cell interference coordination (ICIC), enhanced ICIC (eICIC), orcoordinated multi-point (CoMP) transmission for the LPNs (or other macronodes) in the coordination set. The macro node may not provide ICIC,eICIC, or CoMP for the LPNs or other macro nodes outside thecoordination set. A mobile device in communication with the macro node(or within a coverage area of the macro node) can receive coordinationset information from the macro node. The coordination set informationcan include identifiers of LPNs in the coordination set, including atleast one LPN identifier of the at least one LPN.

The macro node can request that mobile devices in communication with themacro node apply a specified reference signal (RS) biasing. The macronode may request the application of the specified RS biasing when themacro node is experiencing a heavy traffic load in an attempt to offloadtraffic to the LPNs within the HetNet. The mobile device may receivereference signals, such cell specific reference signals (CRS) or channelstate information reference signals (CSI-RS), from LPN located nearbythe mobile device. The mobile device can measure a power or quality of amacro node's RS and can measure a power or quality of LPNs' RS. A RSmeasurement can include a reference signal received power (RSRP), areference signal received quality (RSRQ), or a combination of RSRP andRSRQ. The mobile device can compare the macro node's RS measurementswith the LPNs' RS measurements. The mobile device may associate with themacro node or the LPN with a higher power quality RS measurement. Themobile device can apply the specified RS biasing (or RS power offset orRS quality offset) to either effectively lower the macro node's RSmeasurements or effectively raise the LPN's RS measurements, so thatsome LPNs with a lower power or lesser quality measurement prior to thebiasing can appear to have a higher power or better quality measurementthan the macro node after the biasing. With the application of specifiedRS biasing, some mobile devices may be handed-over or offloaded from themacro node to the LPNs that appeared to have a higher power or betterquality measurement than the macro node. As a result of the specified RSbiasing, the LPN's range expands and more mobile devices re-associatewith LPN instead of maintaining the association with the macro node.Also as a result of the specified RS biasing, the macro node can reducethe mobile devices in direct communication with the macro node andoffload mobile devices to the LPNs. The mobile device may apply thespecified RS biasing to an LPN RS measurement when an LPN identifierrepresenting the LPN is within the received coordination setinformation. The mobile device can associate with the LPN when the LPNRS measurement with the specified RS biasing exceeds an associationthreshold. ICIC, eICIC, or CoMP may be applied to the nodes within thecoordination set to manage the low power conditions of the LPN, enhancethe signal of the LPN, and/or reduce the interference from other nodesand devices. The mobile device may ignore the specified RS biasing to anLPN RS measurement when an LPN identifier for the LPN is not within thereceived coordination set information. If the LPN in not with the samecoordination set as the macro node, ICIC, eICIC, or CoMP may be lesseffective to manage the low power conditions of the LPN, enhance thesignal of the LPN, and/or reduce interference from other nodes anddevices.

The following provides additional details of the examples. FIG. 1illustrates a heterogeneous network (HetNet) with a first high powermacro node 410A (or macro-eNB) with a first backhaul communication link418A with a first lower power node 420A (micro-eNBs, pico-eNBs,femto-eNBs, home eNBs [HeNBs], remote radio head [RRH], or relay node).The HetNet can include a second high power macro node 410B (ormacro-eNB) with a second backhaul communication link 418B with a secondlower power node 420B (micro-eNBs, pico-eNBs, femto-eNBs, home eNBs[HeNBs], remote radio head [RRH], or relay node). The backhaulcommunication link can be a wired, wireless, or optical fiberconnection. The backhaul communication link may use X2 signaling. Thebackhaul communication link can be used to apply interference mitigationor signal coordination between the macro node and the LPNs in acoordination set. HetNets can be used to optimize performanceparticularly for unequal user or traffic distribution and improvespectral efficiency per unit area of a cell. HetNets can also achievesignificantly improved overall capacity and cell-edge performance.Enhanced inter-cell interference coordination (eICIC) can be used tocoordinate resources between the macro node and the low power node (LPN)in the HetNet and reduce interference. Generally, eICIC can allowinterfering nodes to coordinate on transmission powers and/or spatialbeams with each other in order to enable control and data transmissionsto their corresponding mobile devices. Enhanced biasing for HetNetsystems can be used with interference mitigation techniques, such asCoMP or eICIC.

The HetNet (and homogeneous network) can include regular (planned)placement of macro nodes 410A and 410B that can typically transmit athigh power level, for example, approximately 5 watts (W) to 40 W, tocover the macro cell 412A and 412B. The HetNet can be overlaid with lowpower nodes (LPNs) 420A and 420B, which may transmit at substantiallylower power levels, such as approximately 100 milliwatts (mW) to 2 W. Inan example, an available transmission power of the macro node may be atleast ten times an available transmission power of the low power node. ALPN can be used in hot spots or hot-zones, referring to areas with ahigh wireless traffic load or high volume of actively transmittingwireless devices. A LPN can be used in a microcell, a picocell, afemtocell, and/or home network. The microcell can be located in a mall,a hotel, or a transportation hub. The picocell can be located in smallto medium size structures such as offices, shopping malls, trainstations, stock exchanges, or in-aircraft. The femtocell can be locatedin small structures such as a home or a small business.

In an example, a microcell can have a range less than two kilometers(km) and a picocell can have a range within 200 meters (m). In anotherexample, a femtocell can support up to 16 active mobile devices and canhave a range within 50 m. In an example, a LPN may have a power lessthan 24 decibels relative to 1 milliwatt (dBm) for 1 antenna, less than21 dBm for 2 antennas, and less than 18 dBm for 4 antennas. The decibel(dB) is a logarithmic unit that indicates the ratio of a physicalquantity (usually power or intensity) relative to a specified or impliedreference level. A ratio in decibels is ten times the logarithm to base10 of the ratio of two power quantities. The power relative to 1milliwatt (mW) can be represented by dBm (dB(mW)). In another example, aHeNB may have a power less than 20 dBm for 1 antenna, less than 17 dBmfor 2 antennas, and less than 14 dBm for 4 antennas. The HeNB canperform many of the functions of the eNodeB, but the HeNB can beoptimized or designed for use in a home or an office. A RRH may be usedin a centralized, cooperative, or cloud radio access network (C-RAN),where the transmission station (or eNodeB) functionality can besubdivided between a base band unit (BBU) processing pool and a remoteradio unit (RRU) or a remote radio head (RRH) with optical fiberconnecting the BBU to the RRU. A relay node may be used to decode andforward or repeat the signaling of a macro node.

A LPN 420A or 420B can have a standard cell range 422A or 422B (or innercell range) or a cell range expansion 424A or 424B (or cell rangeextension, edge cell range, or cell-edge range). Due to the closerproximity of the mobile device to the LPN, the mobile device within thestandard cell range of the LPN may experience less interference from themacro node and other sources than a mobile device within the cell rangeextension but outside the standard cell range. The standard cellcoverage or range (or center cell range) can represent an area in space(a geographic area) near the transmitting station where the transmissionpower and signal can be strong and a co-channel interference can beminimal. A cell range expansion (CRE) can be area near to the boundaryof the cell where the transmission power and signal is weaker than asignal in the standard cell and the co-channel interference can be moresignificant. In an example, the first macro node 410A can generate acell range expansion in the first LPN 420A and the second LPN node byrequesting that mobile devices within the first macro node's coveragearea perform biasing, such as RS biasing.

The cell range expansion of LPNs can be due to RS biasing requested bythe macro nodes. RS biasing can apply an offset to the RS measurementsallowing a LPN with a signal strength weaker than the macro node toassociate with the mobile device. In an example, the RS biasing can havea range greater than 0 dB to about 6 dB. In another example, the RSbiasing can have a range greater than 0 dB to about 16 dB.

Association (or handover) biasing can be an effective means to achievethe load balancing in non-uniform heterogeneous network deployments. Theload balancing can be provided by coverage (or range) expansion at LPNs(low transmission power nodes). The range expansion can be virtuallyachieved by biasing of the mobile device association metric for LPNs bysome value which may be signaled from the macro node to the mobiledevice via higher layers, such as radio resource control (RRC)signaling. The mobile device association metric can include a referencesignal received power (RSRP) or a reference signal received quality(RSRQ). The load balancing can introduce sever interference conditionsfor mobile devices located in the range expansion zone. In order toprovide reasonable throughput performance for such mobile devices,interference mitigation schemes, such as DL eICIC or CoMP, can beapplied at the macro node (an overlay high transmission power node oraggressor node).

The association can refer to the mobile device's direct wirelesscommunication with a node, either a macro node or LPN. A re-associationcan include transferring a mobile device's direct wireless communicationfrom one node to another node. The both nodes in the re-association maybe within a coordination set or the nodes in the re-association may bein different coordination sets. A handover can refer to a transfer ofthe mobile device's direct wireless communication from a first node in afirst coordination set to a second node in a second coordination set.

In an example, association biasing may not account for interferencemitigation scheme parameters, such as a coordination set. In particular,association biasing applied at the mobile device for LPNs regardless ofthe coordination set that the LPNs belong to can reduce theeffectiveness of the interference mitigation, such as DL eICIC or CoMP.The coordination set (or cluster) can be defined as a set of nodesconnected with each other via backhaul link and performing coordinatedtransmissions.

FIG. 1 illustrates association biasing being applied at the mobiledevice 430 to the second LPN 420B in a second coordination set, wherethe mobile device is associated (and in direction communication 440A)with the first macro node 410A in a first coordination set. The mobiledevice may receive a first macro node transmission 440A from the firstmacro node and a second LPN transmission 450B from the second LPN. Inthe example illustrated in FIG. 1, the first LPN 420A is in the firstcoordination set with the first macro node, and the second LPN is in thesecond coordination set with the second macro node 420B. The twocoordination sets can generate independent transmissions, performindependent coordination, and/or perform independent interferencemitigation from each other. In the example, the mobile device may beoriginally located in the coverage area of the first macro node, whichcan indicate that the mobile device receives the strongest power fromthe first macro node. After applying a range expansion, via associationbiasing, such as RS biasing, the mobile device can reside in the rangeexpansion zone of the second LPN, which can belong to the anothercoordination set, such as the second coordination set. Interferencemitigation for the mobile device may be performed for the secondcoordination set, while the interference suppression from the strongestinterferer (the first macro node) may not be achieved, due toindependent coordination decision at the first coordination set and thesecond coordination set.

Association biasing, and hence range expansion of LPNs, may be appliedto LPNs within the macro node's coordination set without applyingassociation biasing to LPN outside the macro node's coordination set toimprove performance of the mobile devices after the re-association withthe LPNs. In an example, the macro node can inform the mobile devices ofa specified association biasing value, such as a RS biasing value, andthe LPNs belonging to the same coordination set as the macro node (inthe coordination set information). The range expansion can be applied atthe mobile for a restricted set of LPNs belonging to the samecoordination set (or cooperation set) of the macro node. LPNs outsidethe restricted set may not receive the range expansion.

For example, FIG. 2 illustrates a second mobile device 430A applyingrange expansion 424A for the first LPN node 420A in a same coordinationset as the first macro node 410A, and a first mobile device 430B notapplying range expansion (or maintaining a standard range 422B) for thesecond LPN node 420B in a different coordination set as the first macronode. The first mobile device may receive afirst-macro-node-to-first-mobile-device transmission 440A from the firstmacro node and a second LPN transmission 450B from the second LPN. Thesecond mobile device may receive afirst-macro-node-to-second-mobile-device transmission 442A from thefirst macro node and a first LPN transmission 450A from the first LPN.Both the first mobile device and the second mobile can receive thecoordination set information (for a first coordination set) for the LPNs(or other nodes) associated with the first macro node. Both the firstmobile device and the second mobile can receive a request to apply aspecified RS biasing. The request can include the specified RS biasingvalue or the mobile device can apply a predetermined RS biasing valuestored within the mobile device. For example, the specified RS biasingcan be a 3 dB value to be applied to a RSRP measurement. An RSRP can bemeasured in dBm and can have a range of −140 dBm to −44 dBm. The firstmobile device can generate (through a measurement) a first RSRP for thefirst macro node to be −80 dBm and generate a second RSRP for the secondLPN to be −82 dBm. Because the first RSRP has a higher value than thesecond RSRP, the first mobile device associates with the first macronode. The second mobile device can generate (through a measurement) athird RSRP for the first macro node to be −81 dBm and generate a fourthRSRP for the first LPN to be −83 dBm. Because the third RSRP has ahigher value than the fourth RSRP, the second mobile device associateswith the first macro node. Since the first LPN is in the samecoordination set as the first macro node, the specified RS biasing canbe applied to the first LPN. Thus, the RS biasing increases the apparent(or virtual) fourth RSRP value to −80 dBm (−83 dBm RSRP measurement plusthe 3 dB offset of the specified RS biasing). Since, the fourth RSRPvalue is now greater than the third RSRP of −81 dBm, the second mobiledevice may re-associate with the first LPN by transferring communicationfrom the first macro node to the first LPN.

In the example, since the second LPN 420B is in a different coordinationset as the first macro node 410A, the first mobile device 430B may notapply the specified RS biasing to the second LPN 420B. Thus, the firstRSRP value for the first macro node of −80 dBm remains higher than thesecond RSRP value for the second LPN of −82 dBm. Thus, no re-associationfrom the first macro node to the second LPN may occur. The first mobiledevice may remain associated 444A with the first macro device and thesecond LPN may have a standard range (no range expansion), asillustrated in FIG. 3. The second mobile device 430A may bere-associated 454A with first LPN 420A with a range expansion.

In an LTE network, a UE can measure as least two parameters on areference signal, including a reference signal received power (RSRP) anda reference signal received quality (RSRQ). RSRP can be defined as alinear average over the power contributions (in [W]) of the resourceelements that carry cell-specific reference signals (CRS) within aconsidered measurement frequency bandwidth. For RSRP determination theCRS R0 may be used. If the mobile can reliably detect that R1 isavailable, R1 in addition to R0 may be used to determine RSRP. Thereference point for the RSRP may be an antenna connector of the mobiledevice. RSRQ can be defined as the ratio N×RSRP/(E-UTRA carrier RSSI),where N is the number of resource blocks (RBs) of an evolved universalterrestrial radio access (E-UTRA) carrier received signal strengthindicator (RSSI) measurement bandwidth. The measurements in thenumerator and denominator can be made over the same set of resourceblocks. The E-UTRA carrier RSSI can comprise the linear average of thetotal received power (in [W]) observed in OFDM symbols containingreference symbols for an antenna port 0, in the measurement bandwidth,over N number of resource blocks by the UE from all sources, includingco-channel serving and non-serving cells, adjacent channel interference,and/or thermal noise. The reference point for the RSRQ may be theantenna connector of the UE.

Association biasing can also be used in a Coordinated MultiPoint (CoMP)system (also known as multi-eNodeB multiple input multiple output[MIMO]) to improve interference mitigation. FIG. 4A illustrates anexample of an inter-site CoMP system 308. The CoMP system can beillustrated as a plurality of cooperating transmitting stations(outlined with a bold line) surrounded by a plurality of non-cooperatingtransmitting stations. In a CoMP system, the transmitting stations canbe grouped together as cooperating transmitting stations 310A-C inadjacent cells, where the cooperating transmitting stations frommultiple cells can transmit signals to the mobile device 302 and receivesignals from the mobile device. Each transmitting station can servemultiple cells (or sectors) 320A-K, 322A-K, and 324A-K. The cell can bea logical definition generated by the transmitting station or geographictransmission area or sub-area (within a total coverage area) covered bythe transmitting station, which can include a specific cellidentification (ID) that defines the parameters for the cell, such ascontrol channels, reference signals, and component carriers (CC)frequencies. By coordinating transmission among multiple cells,interference from other cells can be reduced and the received power ofthe desired signal can be increased. The cooperating transmittingstations can coordinate transmission/reception of signals from/to themobile device. The transmitting stations outside the CoMP system can benon-cooperating transmitting stations 312D-K. The cooperatingtransmitting stations of each CoMP system can be included in acoordinating set, which can be used in association biasing.

In an intra-site CoMP example illustrated in FIG. 4B, LPNs (or RRHs) ofa macro node 310A may be located at different locations in space, andCoMP coordination may be within a single macro, similar to HetNet. Acell 322A of a macro node may be further sub-divided into sub-cells 330,332, and 334. LPNs (or RRHs) 380, 382, and 384 may transmit and receivesignals for a sub-cell. LPNs (or RRHs) 370 and 374 may transmit andreceive signals for a cell 320A and 324A. A mobile communication device302 can be on a sub-cell edge (or cell-edge) and intra-site CoMPcoordination can occur between the LPNs (or RRHs).

Downlink (DL) CoMP transmission can be divided into two categories:coordinated scheduling or coordinated beamforming (CS/CB or CS/CBF), andjoint processing or joint transmission (JP/JT). With CS/CB, a givensubframe can be transmitted from one cell to a given mobilecommunication device (UE), and the scheduling, including coordinatedbeamforming, is dynamically coordinated between the cells in order tocontrol and/or reduce the interference between different transmissions.For joint processing, joint transmission can be performed by multiplecells to a mobile communication device (UE), in which multipletransmitting stations transmit at the same time using the same time andfrequency radio resources and dynamic cell selection. Two methods can beused for joint transmission: non-coherent transmission, which usessoft-combining reception of the OFDM signal; and coherent transmission,which performs precoding between cells for in-phase combining at thereceiver. By coordinating and combining signals from multiple antennas,CoMP, allows mobile users to enjoy consistent performance and qualityfor high-bandwidth services whether the mobile user is close to thecenter of a cell or at the outer edges of the cell.

Another example provides a method 500 for association biasing at amobile device in a heterogeneous network (HetNet), as shown in the flowchart in FIG. 5. The method includes the operation of receivingcoordination set information from a macro node in the HetNet at themobile device, wherein the coordination set information includes atleast one low power node (LPN) identifier of at least one LPN, as inblock 510. The operation of receiving a request from the macro node atthe mobile device to apply a specified reference signal (RS) biasingfollows, as in block 520. The next operation of the method can beapplying the specified RS biasing at the mobile device to an LPN RSmeasurement derived from a LPN RS received from an LPN having an LPNidentifier in the received coordination set information, as in block530. The method further includes associating the mobile device with theLPN when the LPN RS measurement with the specified RS biasing exceeds anassociation threshold, as in block 540.

Associating the mobile device with the LPN can include associating themobile device with the LPN when the LPN RS measurement with thespecified RS biasing exceeds a macro node RS measurement by apredetermined amount. The predetermined amount can include a toleranceor margin to reduce a likelihood of a re-association between the macronode and LPN with a minor fluctuation in the RS measurement, either LPNRS measurement or the macro node RS measurement. The predeterminedamount can reduce an excessive re-association between the macro node andthe LPN. The mobile device can measure the LPN RS from the LPN togenerate the LPN RS measurement. The mobile device can measure a macronode RS from the macro node to generate the macro node RS measurement.At least one LPN in a coordinating set can have coordinated signalingwith the macro node in the coordinating set. The request from the macronode at the mobile device to apply the specified RS biasing can be usedto offload traffic at the macro node. The mobile device applying thespecified RS biasing to the LPN RS measurement can expand a range forthe mobile device to associate with the LPN. The mobile device canassociate with the LPN and send a re-association request from the mobiledevice to the macro node to associate with the LPN. The re-associationrequest instructs the macro node to offload communication with themobile device to the LPN. The re-association request can include a LPNRS measurement taken by the mobile device. The mobile device canassociate with the LPN and transfer communication from the macro node tothe LPN.

FIG. 6 illustrates an example node and an example mobile device 720 in aHetNet. The node 710 can include a macro node (or macro-eNB) or a lowpower node (micro-eNB, a pico-eNB, a femto-eNB, or a HeNB). The node caninclude a wireless transceiver 712 and a backhaul link transceiver 714.The wireless transceiver of the node can be configured to transmitcoordination set information to a mobile device and transmit a requestto the mobile device in the HetNet to apply a specified reference signal(RS) biasing to a LPN RS measurement derived from a LPN RS received fromthe at least one LPN in the coordination set. The coordination setinformation can include a LPN identifier for the at least one LPN havingcoordinated signaling with the macro node. The backhaul link transceiverof the node can be configured to communicate with the at least one LPNand transfer an association with the mobile device to one of the atleast one LPNs in the coordination set when a LPN RS measurement withthe specified RS biasing exceeds an association threshold.

The mobile device (or UE) 720 can be in communication with a macro node(or macro eNodeB) or a low power node (or micro eNodeB, pico eNodeB,femto eNodeB, or HeNB). In an example, an available transmission powerof the macro node may be at least ten times an available transmissionpower of the LPN.

The mobile device 720 can include a transceiver 722 and a processingmodule 724. The transceiver of the mobile device can be configured toreceive coordination set information from a macro node in the HetNet andreceive a request from the macro node to apply a specified RS biasing.The coordination set information can include at least one LPN identifierof at least one LPN having coordinated signaling with the macro node.The processing module of the mobile device can be configured to applythe specified RS biasing to a LPN RS measurement when a LPN has a LPNidentifier in the received coordination set information, and trigger anassociation with the LPN when the LPN RS measurement with the specifiedRS biasing exceeds an association threshold by a predetermined amount.The predetermined amount can have a value of zero. The associationthreshold can be based on a macro node RS measurement. The processingmodule can be further configured to measure a LPN RS to generate a LPNRS measurement and/or measure a macro node RS to generate a macro nodeRS measurement.

In another example, a transmission station can be in wirelesscommunication with a mobile device. FIG. 7 provides an exampleillustration of the mobile device, such as a user equipment (UE), amobile station (MS), a mobile wireless device, a mobile communicationdevice, a tablet, a handset, or other type of mobile wireless device.The mobile device can include one or more antennas configured tocommunicate with a node, macro node, low power node (LPN), or,transmission station, such as a base station (BS), an evolved Node B(eNB), a base band unit (BBU), a remote radio head (RRH), a remote radioequipment (RRE), a relay station (RS), a radio equipment (RE), or othertype of wireless wide area network (WWAN) access point. The mobiledevice can be configured to communicate using at least one wirelesscommunication standard including 3GPP LTE, WiMAX, High Speed PacketAccess (HSPA), Bluetooth, and WiFi. The mobile device can communicateusing separate antennas for each wireless communication standard orshared antennas for multiple wireless communication standards. Themobile device can communicate in a wireless local area network (WLAN), awireless personal area network (WPAN), and/or a WWAN.

FIG. 7 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the mobiledevice. The display screen may be a liquid crystal display (LCD) screen,or other type of display screen such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen may use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port mayalso be used to expand the memory capabilities of the mobile device. Akeyboard may be integrated with the mobile device or wirelesslyconnected to the mobile device to provide additional user input. Avirtual keyboard may also be provided using the touch screen.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. In the case of program code execution onprogrammable computers, the computing device may include a processor, astorage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, EPROM, flash drive, optical drive,magnetic hard drive, or other medium for storing electronic data. Thebase station and mobile device may also include a transceiver module, acounter module, a processing module, and/or a clock module or timermodule. One or more programs that may implement or utilize the varioustechniques described herein may use an application programming interface(API), reusable controls, and the like. Such programs may be implementedin a high level procedural or object oriented programming language tocommunicate with a computer system. However, the program(s) may beimplemented in assembly or machine language, if desired. In any case,the language may be a compiled or interpreted language, and combinedwith hardware implementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. A system for association biasing at a mobiledevice in a heterogeneous network (HetNet), comprising: a means forreceiving coordination set information from a macro node in the HetNetat the mobile device, wherein the coordination set information includesat least one low power node (LPN) identifier of at least one LPN; ameans for receiving a request from the macro node at the mobile deviceto apply a specified reference signal (RS) biasing; a means for applyingthe specified RS biasing at the mobile device to an LPN RS measurementderived from a LPN RS received from an LPN having an LPN identifier inthe received coordination set information; and a means for associatingthe mobile device with the LPN when the LPN RS measurement with thespecified RS biasing exceeds an association threshold.
 2. The system ofclaim 1, wherein the LPN RS measurement includes a measurement selectedfrom the group consisting of a reference signal received power (RSRP), areference signal received quality (RSRQ), and combinations thereof. 3.The system of claim 1, wherein the specified RS biasing has a rangegreater than 0 decibel (dB) to about 16 dB.
 4. The system of claim 1,wherein the means for associating the mobile device with the LPN furthercomprises a means for associating the mobile device with the LPN whenthe LPN RS measurement with the specified RS biasing exceeds a macronode RS measurement by a predetermined amount.
 5. The system of claim 4,further comprising prior to applying the specified RS biasing at themobile device: a means for measuring a LPN RS from the LPN to generatethe LPN RS measurement; and a means for measuring a macro node RS fromthe macro node to generate the macro node RS measurement.
 6. The systemof claim 1, wherein at least one LPN in a coordinating set hascoordinated signaling with the macro node in the coordinating set. 7.The system of claim 1, wherein the means for associating with the LPNfurther comprises a means for sending a re-association request from themobile device to the macro node to associate with the LPN, wherein there-association request instructs the macro node to offload communicationwith the mobile device to the LPN.
 8. The system of claim 7, wherein there-association request includes a LPN RS measurement taken by the mobiledevice.
 9. The system of claim 1, wherein the means for associating withthe LPN transfers communication from the macro node to the LPN.
 10. Amobile device in a heterogeneous network (HetNet), comprising: atransceiver configured to receive coordination set information from amacro node in the HetNet and receive a request from the macro node toapply a specified reference signal (RS) biasing, wherein thecoordination set information includes at least one low power node (LPN)identifier of at least one LPN having coordinated signaling with themacro node; and a processing module configured to apply the specified RSbiasing to a LPN RS measurement when a LPN has a LPN identifier in thereceived coordination set information, and trigger an association withthe LPN when the LPN RS measurement with the specified RS biasingexceeds an association threshold.
 11. The mobile device of claim 10,wherein the LPN RS measurement includes a measurement selected from thegroup consisting of a reference signal received power (RSRP), areference signal received quality (RSRQ), and combinations thereof. 12.The mobile device of claim 10, wherein the specified RS biasing has arange greater than 0 decibel (dB) to about 16 dB.
 13. The mobile deviceof claim 10, wherein the association threshold is based on a macro nodeRS measurement.
 14. The mobile device of claim 13, wherein theprocessing module is further configured to measure a LPN RS to generatea LPN RS measurement and measure a macro node RS to generate a macronode RS measurement.
 15. The mobile device of claim 10, wherein themobile device includes a user equipment (UE) with an antenna, a touchsensitive display screen, a speaker, a microphone, a graphics processor,an application processor, internal memory, a non-volatile memory port,or combinations thereof.
 16. A macro node in a heterogeneous network(HetNet) having a coordination set including at least one low power node(LPN), comprising: a wireless transceiver configured to transmitcoordination set information to a mobile device and transmit a requestto the mobile device in the HetNet to apply a specified reference signal(RS) biasing to a LPN RS measurement derived from a LPN RS received fromthe at least one LPN in the coordination set, wherein the coordinationset information includes a LPN identifier for the at least one LPNhaving coordinated signaling with the macro node; and a backhaul linktransceiver configured to communicate with the at least one LPN andtransfer an association with the mobile device to one of the at leastone LPNs in the coordination set when a LPN RS measurement with thespecified RS biasing exceeds an association threshold.
 17. The macronode of claim 16, wherein the specified RS biasing has a range greaterthan 0 decibel (dB) to about 16 dB.
 18. The macro node of claim 16,further comprising a processing module configured for implementing anenhanced inter-cell interference coordination (eICIC), coordinatedmulti-point (CoMP), or combination of thereof for the nodes in thecoordination set when the specified RS biasing is requested.
 19. Themacro node of claim 16, wherein the coordinated signaling includes X2signaling or backhaul link signaling via a wired connection, a wirelessconnection, or an optical fiber connection.
 20. The macro node of claim16, wherein the macro node includes a macro evolved Node B (macro-eNB)and the LPN includes a micro-eNB, a pico-eNB, a femto-eNB, or a home eNB(HeNB).